1. Field of the Invention
The present invention relates to indigestible dextrins which are prepared by heat-treating potato starch with addition of an acid and hydrolyzing the resulting starch with alpha-amylase and glucoamylase and which contain dietary fiber and have a low caloric value.
2. Description of the Prior Art
Pyrodextrins are prepared by heating a starch containing several percent of water in the presence or absence of acid. These dextrins include British gum which is obtained by heating the starch at 135.degree. to 218.degree. C. in the absence of acid for 10 to 20 hours, white dextrin which is prepared by heating the starch at 79.degree. to 121.degree. C. in the presence of acid for 3 to 8 hours, and yellow dextrin which is prepared similarly by heating the starch at 150.degree. to 220.degree. C. with addition of acid for 6 to 18 hours.
It is known that these dextrins are consisted of glucose, the component of starch, which consists primarily of 1.fwdarw.4 and 1.fwdarw.6 glycosidic linkages and contains very small amounts of 1.fwdarw.3 and 1.fwdarw.2 glycosidic linkages.
The proportions of these glycosidic linkages are disclosed only in J. D. Geerdes et al., J. Am. Chem. Soc., Vol. 79, 4209 (1957), G. M. Christensen et al., J. Am. Chem. Soc., Vol. 79, 4492(1957) and the literature mentioned below. Methylation analysis of pyrodextrin obtained by heat-treating commercial corn starch with addition of hydrochloric acid reveals that the pyrodextrin comprises at least 57.3% of 1.fwdarw.4 glycosidic linkage fraction (2,3,6-Tri-O-Methyl-D-glucose), 2.6% of 1.fwdarw.6 glycosidic linkage fraction (2,3,4-Tri-O-Methyl-D-glucose), up to 1.2% of 1.fwdarw.3 glycosidic linkage fraction (2,4,6-Tri-O-Methyl-D-glucose), 6.3% of a fraction having both 1.fwdarw.4 and 1.fwdarw.6 linkages (2,3-Di-O-Methyl-D-glucose) and about 20% of a fraction having other glycosidic linkages.
Further R. L. Whistler and E. F. Paschall, Starch Chemistry & Technology, Vol. 1, 430 (965) makes reference to analyzed values of linkage types constituting heat-treated amylopectin and heat-treated amylose which were obtained by separating corn starch into amylopectin and amylose fractions and individually heating the fractions with addition of an acid. The analyzed values were obtained for the heat-treated fractions which were prepared by gelatinizing the starch, then separating the starch into the two fractions and heating the fractions. The form of powder heat-treated therefore differs from that of natural starch, so that the values can not be used directly for comparison. However, in view of the fact that the ratio between the two fractions of usual corn starch is about 8:2, the analyzed values, when calculated for corn starch, correspond to 67% of 1.fwdarw.4 glycosidic linkage fraction-(2,3,6-Tri-O-Methyl-D-glucose), 2.7% of 1.fwdarw.3 glycosidic linkage fraction (2,4,6-Tri-O-Methyl-D-glucose) and 7.8% of a fraction having both 1.fwdarw.4 and 1.fwdarw.6 glycosidic linkages (2,3 Di-0-Methyl-D-glucose).
Tomasik, P. and Wiejak, S., Advance in Carbohydrate Chemistry, Vol. 47, 279-343 (1990) generally describes the latest information as to processes for preparing pyrodextrins.
When analyzed, however, any of commercial pyrodextrins was found to be up to 30% in indigestible content, up to 3% in dietary fiber content, at least 3.1 kcal/g in caloric value 1 and at least 3.1 kcal/g in caloric value 2. When starch was heated under altered conditions to increase these contents, it was possible to increase the indigestible content to about 60% and the dietary fiber content to about 30% and to decrease the caloric value 1 to about 2.7 kcal/g and the caloric value 2 to about 2 kcal/g, whereas the product then contained an increased amount of colored substance, had a stimulative odor, therefore required refining and was not practically useful because of extreme difficulties encountered in refining the product. Accordingly, it is impossible to obtain a dextrin which is at least 75% in indigestible content, at least 20% in dietary fiber content, up to 2.6 kcal/g in caloric value 1 and up to 2 kcal/g in caloric value 2 as contemplated by the present invention.
With respect to the enzymic hydrolysis of pyrodextrins, B. Brimhall, Ind. Eng. Chem., 36, 72 (1944) discloses that when so-called British gum prepared by heating starch in the absence of acid is hydrolyzed with alpha-amylase, the limit of decomposition is 3.5% calculated as maltose, i.e., about 7.4 calculated as DE.
Further U.S. Pat. No. 3,974,032 discloses a hydrolyzate which is prepared from a pyrodextrin obtained with addition of hydrochloric acid and having a degree of branching of 7 to 16% by hydrolyzing the pyrodextrin at 60.degree. to 85.degree. C. To DE of 9 to 20 with alpha-amylase and which is up to 20 in the ratio of weight average molecular weight to number average molecular weight and contains up to 20% of oligosaccharides having a degree of polymerization of 200. However, the patent discloses nothing about hydrolysis with glucoamylase or about dietary fiber.
With improvements in living standards in Japan in recent years, eating habits have changed and become similar to those of American and European people. This trend has resulted in a lengthened average life span and a rapidly aging society with marked increases in degenerative diseases. Manifestly, people have become health-oriented. Attention has, therefore, been directed to dietary fibers and oligosaccharides enhance the function of foods and livestock feeds in that these materials are known to alleviate constipation and other desired biological regulatory functions.
Indigestible substances, such as dietary fibers and oligosaccharides, exhibit various modes of behavior in the digestive tracts producing physiological effects on the living body. First in the upper digestive tract, water-soluble dietary fibers slow the transport of food and delay the absorption of nutrients. Delayed absorption of sugar, for example, suppresses the rise in blood sugar value, consequently lowering insulin requirements. Further, excretion of bile acid is promoted, diminishing the sterol group in the body thereby lowering the cholesterol level of the serum. Other physiological effects through the endocrine system of the body are also reported.
Another feature of these indigestible substances is they are not digested or absorbed by the digestive tract, including the small intestine and reach the large intestine. On reaching the large intestine, oligosaccharides and dietary fibers are partly acted on by enterobacteria yielding short-chain fatty acids, intestinal gases, vitamins, etc. Acidification of the intestinal environment by the short-chain fatty acids condition the intestine. It has also been reported that when absorbed, these short-chain fatty acids are metabolized to provide energy and, simultaneously, inhibit the synthesis of cholesterol. Therefore, ingestible substances are necessary in obtaining these desired physiological effects.
A "dietary fiber hypothesis" suggested by Trowell and Burkitt epidemiologically revealed that there is a negative correlation between the intake of dietary fibers and the onset of non-infectious diseases such as cholelithiasis, ischemic heart diseases, cancer of the large intestine, etc. Thus, insufficient ingestion of dietary fibers is thought to be a cause of degenerative diseases which are said to be diseases of the Western type. The dietary fibers are defined as the "whole group of indigestible components of foods which are not digestible by human digestive enzymes" and are classified into insoluble dietary fibers and water-soluble dietary fibers according to the solubility in water. Of these, water-soluble dietary fibers have attracted attention as materials for functional foods and livestock feeds because of their great physiological function.
For example, it is said that high viscosities inhibit diffusion of sugar, resulting in delayed absorption o sugar and reduction in the rise of blood sugar value, consequently lowering insulin necessity. Further it is said that promoted excretion of bile acid into feces by water-soluble dietary fibers diminishes cholesterol in the serum, and that after reaching the large intestine, the dietary fibers are acted on by enterobacteria to produce lactic acid and acetic acid with these organic acids lowering the pH within the large intestine and preventing cancer of the large intestine.
Examples of such water-soluble dietary fibers include guar gum, glucomannan, pectin and like natural gums which have high viscosity which are difficult to ingest singly in a large amount. Further the addition of these fibers to processed foods encounters problems in preparing the food and presents difficulties with respect to texture. It has therefore long been desired to provide dietary fibers of low viscosity which have the same physiological functions as the above fibers, are easy to ingest and are user-friendly in preparing processed foods.
In recent years in Japan, processed foods, precooked foods, fast foods and the like have found wider use with the maturity of economical environments and the resulting improvements in food processing techniques and distribution techniques. With this trend, diversified information as to the ingestion of foods has become available, and eating habits to fulfill the nutrient requirements are changing to health-oriented dietary habits contemplated for the prevention of nutrition disorders and degenerative diseases due to eating habits. Especially, people of middle or advanced age and young women have much need for low caloric foods, so that low caloric sweeteners and bulking agents for strong sweetening agents have been developed. Among these, low caloric sweeteners include various indigestible oligosaccharides and sugar alcohols, which nevertheless have many problems with respect to the quality, degree of sweetness, oligosaccharide content and likelihood of causing laxation.
The bulking agent available for use with strong sweetening agents such as aspartame is polydextrose only, whereas polydextrose is ingestible in a limited amount, tastes bitter in an acid condition, is hygroscopic and therefore has problems. In view of the situation described, it has been desired to provide a low caloric bulking agent which fulfills the requirements for use as a food and which is usable for sweeteners and the like with safety.
On the other hand, starch is used in large quantities in various processed foods as a food material. Useful food materials of these types include starch and starch products such as pregelatinized starch, pyrodextrin, and its derivatives, glucose, corn syrup solids and maltodextrin. However, a majority of these starch products are not higher than 5% in the content of indigestible component and at least 3.9 kcal/g in caloric value, so that among starches and like materials, only pyrodextrin appears useful as a dietary fiber and low caloric material. Heat-treated starch (pyrodextrin) will hereinafter be referred to merely as "dextrin".